Coaxial transmission line termination



May 11, 1954 o. o. FlET 2,678,428

COAXIAL TRANSMISSION LINE TERMINATION Filed Sept. 7, 1949 15 In "1 I 23lNVENTOF} Owen 0.1 161 BY f I ATTORNEY Patented May 11, 1954 R ISSION LNE. TERMINATION Q cn O an o Fiet, O yn, N. J., assignor to RadiCorporation f me ica, a c rporati n of D laware Application Septemb I,1949, Serial. 114,400

6 Claims- 1 The invention relates to coaxial transmission lines and itparticularly pertains to an improved arrangement for terminatingopen-ended coaxial transmission line sections.

Open-ended coaxial transmission lines are very frequently employed inhigh frequency radio in stailations asimpedance matching devices, r650!nant circuit elements, notch filters, and the like,to great advantage.While theoretically the known arrangements are equally applicable tohigh gr power installations as well as low power installations. it hasbeen found. that in installations of 10 kw. and higher ower, thedifferential thermal expansion between the inner and outer conductors ofan open-ended coaxial transmission line has a detrimental effect .on thetuning of the line.

It. is: an object of the invention to provide a terminating arrangementfor an open-ended coaxial transmission line which-willnot be affected bytemperature variations.

It. is another object of the invention to provide a termination for anopen-ended coaxial transmission line eliminating the deleterious effectscaused by differential thermal expansion between the inner and outerconductors of the. line.

it is a further object of the inventionto provide a simple andinexpensive termination for a coaxial transmission line which is readilyj-111st able and completely reliable in. operation.

These and other obi ects of the invention which appear as. thespecification pro esse are attained by means of a device consistingessendollar of. a con uctive sleeve placed over the en of the rconductor of an open-ended coaxi l trshsm ion line, which sleeve i restin y the outer conductor on ,.an mea s. e p v d to maintain elec ric lcon act between he i n conduct and the sleeve, m anwhile permit ing heinner conduc o to move within e l e accordance i h temper u e variationswhereby the effect of differential thermal expansion between the innerand outer conductors is elim n t The inv n ion will be descri ed with fr nce to the accompanyin dr win form n a a t of the specification and inwhich:

Fig. l is an illustration, partly in cross-section, of an embodiment ofthe invention;- and Fig. 2 is an illustration of an alternate embodimentof the invention.

Referring to Fig. 1, there is shown an end portion of a coaxialtransmissionline ll having a sheath conductor l3 and a concentricallyarranged inner conductor l5ligidly held in place by means of a pluralityof insulator members I1.

' faci itate such a preferably but not necessarily in the form ofansnular plugs which are held inplace either by crimping the sheathconductor as shown at lfl b y pins as shown at 2 I, or any other methodknown to those skilled in the art. In prior art-arrange ments, the endof conductor 15 is allowed to ride in the aperture of insulator H wherethe expansion and contraction of inner conductor 15 due to temperaturevariations, being different from that of. the sheath conductor,wonldintroduce dole, terious. efiects on the tuning of: the circuit inwhich the coaxial transmission line section is employed.

According to the invention, these disadvantages are eliminated byproviding a conductive sleeve '23. which is. restrained from movement inthe axial direction by insulating member 11- and sheath conductor [3. Inthe preferred arrange.- ment, insulator l1 and sleeve '23 are fastenedto.- gether by slightly undercutting sleeve 23 for a portionintermediate its ends which is just sum.- .ciently long enough toaccommodate the thick.- ness .of insulator H which is forced over theTB? mainder of sle ve 23. Sleeve '23, which may be a tubular member orwhich may be entirely close at one end as is shown, has. an annulargroove 21 .milledin the inner wall thereof to accepts toroid l co l spin 219 throosh t whi h inner conductor 1.5 o oo. line .1! slides to povide .cl ct leeve 23 su ta le for the low s encount r d hea th e d o transm ss on line. Prefe a l or ElQQ e :25 i f sui icicn epth tha onl ali ht sort-ion f coil sh ine 23. p otrude into bo e 25 oi s ee 23.. rdeto retain the co oer e to the ins rtion o inner o ductor l5 o .25 analso to maintain the overalldimension of sleeve 23- at a minimum.While-the a ran ementhe h ss' li preferably in erted in o t e. auditslocation detcrmi ed l r 11. to sheath .c. an ally prior conductor 13 tofastenin 11 811 of the. cos: t

into sleeve 2:3 trans accommodate some form of tool, such as a tong.-like spanner, which may he used to slide the assembly comprisinginsulator ll and sleeve -23 in the axial direction in order to determinethe optimum location of the sleeve.

Since it will be obvious that the tuning oi such a transm sio l i om wht c l, the adjustment of the device may be more readily and accuratelymade with the arrangement shown in Fig. 2, wherein a plurality of slots3| are milled into sheath conductor 13 of transmission line I I in adirection diagonally to the axis thereof and insulating member I! isheld in place by means of studs 33 passing through slots 3 i. Forclarity, the inner conductor l5, sleeve 23 and coil spring 29 areomitted from Fig. 2. Plate members 35 made of suitable resilientmaterial are placed over studs 33 to serve both as coverings for slots3| and also as lock washers for acorn nuts 36. The arrangement is tunedby loosening nuts 36 and exerting force to rotate member ll about theaxis of transmission line H, which rotation will cause studs 33 to bearagainst the sides of slots 3i and force member IT to move in the axialdirection. Once the tuning of the coaxial line section has beendetermined, nuts 36 are tightened and the transmission line will remainproperly tuned despite temperature variations. The ratio of axial torotational movement is varied by varying the angle at which slots 3| aremilled, the optimum angle being that which will provide the desiredrange of tuning with the maximum rotation allowable under the particularcircumstances.

While the invention has been described in terms of express embodiments,it is to be understood that obvious modifications thereof will besuggested to those skilled in the art without departing from the spiritand scope of the invention.

I claim:

1. A coaxial transmission line section incorporating means to adjust thelength thereof without deleterious effect thereto by reason of relativethermal expansion of the inner and sheath conductors of said linesection, the sheath conductor of said line section having elongatedslots arranged therein diagonally of the axis of said sheath conductor,a sleeve member surrounding the inner conductor of said line section, aninsulating member fixed to said sleeve member, guid members fixed tosaid insulating member and arranged in the slots in said sheathconductor to cause said insulating member and said sleeve member to moveaxially in response to rotation thereof initially to adjust the lengthof said transmission line section, and a coil spring interposed betweensaid sleeve member and said inner conductor to provide electricalcontact therebetween without restraining relative movement in the axialdirection therebetween to main tain the length of said transmission linesection substantially constant as initially adjusted.

2. An open-ended coaxial transmission line section incorporating meansto adjust the length thereof without deleterious effect thereto byreason of relative thermal expansion of the inner and sheath conductorsof said line section, the sheath conductor of said line section havingelongated slots arranged therein diagonally of the axis of said sheathconductor, a sleeve member surrounding the inner conductor of said linesection and having an annular groove in the inner Wall thereof, aninsulating member fixed to said sleeve member, stud members fixed tosaid insulating member and arranged in the slots in said sheathconductor to cause said insulating member and said sleeve member to moveaxially in response to rotation thereof initially to adjust the lengthof said transmission line section, and a coil spring arranged in theannular groove of said sleeve member to provide electrical contactbetween said sleeve member and said inner conductor without restrainingrelative movement 4 in the axial direction therebetween to maintain thelength of said transmission line section substantially constant asinitially adjusted.

3. An open-ended coaxial transmission line section incorporating meansto adjust the length thereof without deleterious effect thereto byreason of relative thermal expansion of the inner and sheath conductorsof said line section, the sheath conductor of said line section havingelongated slots arranged therein diagonally of the axis of said sheathconductor, a sleeve member surrounding the inner conductor of said linesection and having an annular groove in the inner wall thereof, aninsulating member fixed to said sleeve member, stud members fixed tosaid insulating member and arranged in the slots in said sheathconductor to cause said insulating member and said sleeve member to moveaxially in response to rotation thereof initially to adjust the lengthof said transmission line section, locking means arranged on said studmembers to fix the position of said sleeve with respect to said sheathconductor, and a coil spring arranged in the annular groove of saidsleeve member to provide electrical contact between said sleeve memberand said inner conductor without restraining relative movement in theaxial direction therebetween to maintain the length of said transmissionline section substantially constant as initially adjusted.

4. A terminating device for a coaxial transmission line having an innerconductor and a sheath conductor, the sheath conductor of said coaxialtransmission line having elongated slots arranged therein diagonally ofthe axis of said sheath conductor, including a sleeve member surroundingthe inner conductor of said line, an electrically spacing member fixedto said sleeve member to space the same from said sheath conductor,guide members fixed to said electrically spacing member and arranged inthe slots in said sheath conductor to cause said spacing memher and saidsleeve member to move axially in response to rotation thereof initiallyto adjust the length of said coaxial transmission line, and a resilientelement interposed between said sleeve member and said inner conductorto provide elec-'- trical contact therebetween without restrainingrelative movement in the axial direction therebetween to maintain thelength of said transmission line substantially constant as initiallyadjusted.

5. A terminating device for a coaxial transmission line having aconductive inner member and. a sheath conductor, the sheath conductor ofsaid coaxial transmission line having elongated slots arranged thereindiagonally of the axis of said sheath conductor, including a sleevemember surrounding the conductive inner member of said coaxialtransmission line, one of said members having an annular groove in awall thereof, an insulating member fixed to said sleeve member, studmembers fixed to said insulating member and arranged in the slots insaid sheath conduetor to cause said insulating member and said sleevemember to move axially in response to rotation thereof initially toadjust the length of said coaxial transmission line, and a resilientelement arranged in said annular groove to provide electr cal contactbetween said sleeve memher and said conductive inner member withoutrestraining relative movement in the axial direction therebetween tomaintain the length of said transmission line section substantiallyconstant as initially adjusted.

6. A terminating device for an open-ended coaxial transmission linehaving a conductive inner member and a sheath conductor, the sheathconductor of said transmission line having elongated -slots arrangedtherein diagonally of the axis of said sheath conductor, including asleeve member surrounding the conductive inner member of said coaxialtransmission line, one of said members having an annular groove in acontiguous Wall thereof, an insulating member fixed to said sleevemember, stud members fixed to said insulating member and arranged in theslots in said sheath conductor to cause said insulating member and saidsleeve member to move axially in response to rotation thereof initiallyto adjust the length of said coaxial transmission line, and lockingmeans arranged on said stud members to fix the position of said sleevewith respect to said sheath conductor, and a resilient element arrangedin the annular groove of said one member to provide electrical contactbetween said sleeve References Cited in the file of this patent UNITEDSTATES PATENTS Number Name Date 1,696,947 Flaherty Jan. 1, 19292,044,580 Leach June 16, 1936 2,082,860 Walter June 8, 1937 2,103,515Conklin et al. Dec. 28, 1937 2,143,671 Zottu Jan. 10, 1939 2,280,728Streib Apr. 21, 1942 2,379,047 Thomas June 26, 1945 2,449,479 Hopper eta1 Sept. 14, 1948 2,542,974 Abbot Feb. 27, 1951 2,548,881 Ferrill Apr.17, 1951

